*2.3. FTIR Spectroscopy of CS/PVOH/HNT and CS/PVOH/TO@HNT Films*

In Figure 3 representative spectra of pure CS/PVOH, CS/PVOH/HNT, and CS/PVOH/TO@HNT are observed. *Gels* **2022**, *8*, x FOR PEER REVIEW 6 of 25

**Figure 3.** FTIR spectras of neat CS/PVOH film (1) as well as CS/PVOH/HNT (2), and CS/PVOH/TO@HNT (3) films for comparison. **Figure 3.** FTIR spectras of neat CS/PVOH film (1) as well as CS/PVOH/HNT (2), and CS/PVOH/TO@HNT (3) films for comparison.

FTIR spectra of pure CS/PVOH (see line (1) in Figure 3) are a combination of both CS and PVOH reflections. The large band at 3443 cm−1 is assigned to O–H groups stretching both presented in CS and PVOH and to N–H groups stretching of CS. The same band is also assigned to the intra- and inter-molecular hydrogen bonds of the CS/PVOH matrix.Τhe band at2896 cm−1 is assigned to C–H asymmetric and symmetric stretching from CH<sup>2</sup> and CH groups. The band at 1637–1644 cm*−*<sup>1</sup> is assigned to the associated water, C–OH from the glycosidic units of CS chains, and also the presence of residual N-acetyl groups (C=O stretching of amide I), and N-H in-plane deformation coupled with C–N stretching of amide II (secondary amide) from CS. The band at 1154 cm−1 is assigned to the FTIR spectra of pure CS/PVOH (see line (1) in Figure 3) are a combination of both CS and PVOH reflections. The large band at 3443 cm−<sup>1</sup> is assigned to O–H groups stretching both presented in CS and PVOH and to N–H groups stretching of CS. The same band is also assigned to the intra- and inter-molecular hydrogen bonds of the CS/PVOH matrix.The band at2896 cm−<sup>1</sup> is assigned to C–H asymmetric and symmetric stretching from CH<sup>2</sup> and CH groups. The band at 1637–1644 cm−<sup>1</sup> is assigned to the associated water, C–OH from the glycosidic units of CS chains, and also the presence of residual N-acetyl groups (C=O stretching of amide I), and N-H in-plane deformation coupled with C–N stretching of amide II (secondary amide) from CS. The band at 1154 cm−<sup>1</sup> is assigned to the glycosidic linkage (asymmetric bridge stretch) [54].

glycosidic linkage (asymmetric bridge stretch) [54]. In the FTIR spectra of CS/PVOH/HNT and CS/PVOH/TO@HNT systems (see lines (2) and (3) in Figure 3) it additionally obtained the characteristic reflection band at 3620 cm*−*<sup>1</sup> assigned to O-H groups in the internal HNT's surface. With a careful glance, it is obtained that the main difference between FTIR plots of CS/PVOH/HNT and CS/PVOH/TO@HNT is that in the case of CS/PVOH/HNT plot the band of O-H and N-H group stretching at 3443 cm*−*<sup>1</sup> is more intense than the same band of CS/PVOH/TO@HNT plot. This implies a higher interaction between OH groups of the CS/PVOH matrix and OH groups of pure HNT than OH groups of the CS/PVOH matrix and modified In the FTIR spectra of CS/PVOH/HNT and CS/PVOH/TO@HNT systems (see lines (2) and (3) in Figure 3) it additionally obtained the characteristic reflection band at 3620 cm−<sup>1</sup> assigned to O-H groups in the internal HNT's surface. With a careful glance, it is obtained that the main difference between FTIR plots of CS/PVOH/HNT and CS/PVOH/TO@HNT is that in the case of CS/PVOH/HNT plot the band of O-H and N-H group stretching at 3443 cm−<sup>1</sup> is more intense than the same band of CS/PVOH/TO@HNT plot. This implies a higher interaction between OH groups of the CS/PVOH matrix and OH groups of pure HNT than OH groups of the CS/PVOH matrix and modified TO@HNT.

A Scanning Electron Microscopy (SEM) instrument was used for the surface/crosssection morphology investigation of the pure CS/PVOH film as well as of the CS/PVOH/HNT and CS/PVOH/TO@HNT nanocomposite films. The results confirmed that both HNT and the TO@HNT hybrid nanostructures were homogeneously dispersed in the polymer matrix. The chemical elements of the pure and the final nanocomposite active packaging films were identified by carrying out an Energy dispersive spectrometer

The SEM images in Figure 4a,b show the expected smooth morphology of the neat polymer. The EDS spectra in Figure 4c certify the existence of carbon (C), and oxygen (O).

(EDS) analysis on the surface of the materials.

TO@HNT.
